Field of the Invention
The invention relates to a method for varying the spring rigidity of an elastomer mount, in particular an engine mount for motor vehicles, having two rubber bodies that can be at least intermittently loaded simultaneously, and a corresponding elastic mount.
Modern engine mounts generally have the task both of absorbing the various static and dynamic engine holding forces occurring during vehicle operation and damping the resultant low-frequency engine vibrations, and of suppressing the transmission of acoustical vibrations that are propagated from the engine to the body and thus to the passenger compartment of a motor vehicle. That means that the mount must have different properties, in terms of rigidity and the loss angle of damping, in the low-frequency and high-frequency ranges. In the construction of an engine mount, that dictates major compromises, which under unfavorable conditions may be far from optimum. One possibility for lessening the incident deviations from the optimum is to use known hydraulically damped engine mounts, which effect major damping of low-frequency vibrations and simultaneously make purposeful decoupling of the high-frequency vibrations possible. However, with such mounts as well, the properties in the low and high-frequency ranges cannot be adjusted independently, so that adaptation to the various required values becomes very complicated and expensive. Moreover, such hydraulically damped engine mounts generally have a disadvantage which is that a variation in the dynamic rigidity occurs only in the axial or in other words vertical direction, while in the radial direction the rigidity remains largely unchanged. A controlled change in rigidity that is adapted to applicable operating conditions is not possible.
It is accordingly an object of the invention to provide a method for varying the spring rigidity of an elastomer mount and a corresponding mount, which overcome the hereinaforementioned disadvantages of the heretofore-known methods and devices of this general type and which, based on a pure elastomer mount, discloses a method with which the spring rigidity and damping of such a mount can be varied as a function of predetermined operating parameters, in such a way that at low rpm and therefore high vibration amplitudes, particularly when idling, such a mount is relatively soft, while at higher operating rpm it is relatively hard.
Such a mount is known in principle from British Patent No. 1 408 584, in which elastomer bodies extending in concentric rings with respect to one another having a parabolically inclined overall surface are provided with a mount plate extending approximately parallel to them, tut in which a gap between it and the rubber bodies increases steadily toward the rim. When a load is introduced, radially farther-outward rubber bodies engage the mount plate in succession, so that the rigidity of the mount is increased in stages. However, neither varying the rigidity nor individual engagement of various elastomer bodies is possible.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for varying the spring rigidity of an elastomer engine mount for motor vehicles, which comprises bringing one of two at least intermittently simultaneously loadable parallel-connected spring or rubber bodies into continuous engagement with supports for the one spring body and bringing the other of the two spring bodies into intermittent contact with supports for the other spring body as a function of predetermined operating parameters, for absorbing induced forces in parallel with the two spring bodies, and connecting the other spring body in parallel with a force brought to bear separately from the outside for causing the other spring body to contact the supports for the other spring body.
In accordance with another mode of the invention, there is provided a method which comprises selecting different hardnesses for the two spring bodies, and only intermittently bringing the spring body with the greater hardness into effective engagement.
In accordance with a further mode of the , there provided a method which comprises connecting the two spring bodies in parallel as a function of engine rpm.
In accordance with an added mode of the invention, there is provided a method which comprises bringing the force for the parallel connection to bear by means of a pressure cushion to be acted upon hydraulically.
In accordance with an additional mode of the invention, there is provided a method which comprises bringing the force for the parallel connection to bear with mechanically adjusting means.
With such a method it is accordingly possible to vary the spring rigidity of a pure rubber mount between a "soft" and a "hard" characteristic, depending on given requirements and operating parameters.
With the objects of the invention in view, there is also provided an elastic engine mount for motor vehicles, comprising an engine mount plate, a support plate to be fixed to a vehicle body, a hollow-cylindrical spring body, a solid-cylindrical spring body or block having a lower end surface, the spring bodies being disposed concentrically relative to one another between the plates, and a diaphragm disposed between the lower end surface of the solid-cylindrical spring body and the support plate for defining a hollow chamber between the diaphragm and the support plate, the hollow chamber operatively connecting the solid-cylindrical spring body with the plates upon forced introduction of hydraulic fluid into the hollow chamber.
With the objects of the invention in view, there is furthermore provided an elastic engine mount for motor vehicles, comprising an engine mount plate, a support plate to be fixed to a vehicle body, a hollow-cylindrical spring body, a solid-cylindrical spring body or block having a lower end surface, the spring bodies being disposed concentrically relative to one another between the plates, a mechanical plunger disposed between the lower end surface of the solid-cylindrical spring body and the support plate, a threaded bolt engaging the mechanical plunger, and a control motor for driving the threaded bolt and operatively connecting the solid-cylindrical spring body with the plates.
In accordance with another feature of the invention, the solid-cylindrical spring body has a shorter axial length than the hollow-cylindrical spring body.
In accordance with a further feature of the invention, the solid-cylindrical spring body has a lower end wall with an annularly protruding extension, and there is provided a sleeve being fixed on the support plate and having a drawn-in rim for engaging the extension from behind in a spaced-apart manner.
In accordance with an added feature of the invention, the extension is formed by a metal plate vulcanized on the solid-cylindrical spring body.
In accordance with still another feature of the invention, the metal plate has a lower surface covered with an elastic rubber layer.
In accordance with an additional feature of the invention, there is provided a sleeve being fixed on the support plate and having a base, the diaphragm having a periphery being fastened in a fluid-tight manner between the support plate and the base of the sleeve, and the support plate having an adjustable inlet for a hydraulic fluid.
After a fluid is forced into the hollow chamber thus formed beneath the diaphragm, the solid-cylindrical spring body is thus pressed against the drawn-in rim of the sleeve, so that a force-locking connection is established, and so both spring bodies then absorb forces induced parallel to one another. A force-locking connection is one which connects two elements together by force external to the elements, as opposed to a form-locking connection which is provided by the shapes of the elements themselves.
In accordance with yet another feature of the invention, the force generated by the pressure of the fluid is greater than the incident operating forces, in the form of the static load to be supported and the dynamic operating forces.
In accordance with yet a further feature of the invention, the hydraulic pressure is approximately 5 bar.
In accordance with yet an added feature of the invention, there is provided a cup-shaped flange plate secured beneath the support plate and centrally carrying the control motor, the threaded bolt penetrating the flange plate and the support plate, and the plunger being box-like and having a top to be forced against the solid-cylindrical spring body.
In accordance with still a further feature of the invention, the box-like plunger has an underside and two ribs protruding from the underside and penetrating guide slits formed in the support plate.
In accordance with yet an additional feature of the invention, the hollow-cylindrical spring body is disposed outside the solid-cylindrical spring body, the outer hollow-cylindrical spring body has a Shore A hardness of approximately 40, and the inner solid-cylindrical spring body has a Shore A hardness of approximately 65. This is done in order to provide an optimal ratio of spring rigidities of parallel-connected spring bodies and only one acted-upon spring body.
In accordance with again another feature of the invention, the ratio of the axial to the radial rigidity of the mount is approximately 4.5. In order to attain this rigidity ratio, in accordance with again a further feature of the invention, the hollow-cylindrical spring block can additionally be subdivided axially, approximately centrally, by a rigid intermediate ring.
In accordance with again a further feature of the invention, different radial rigidities are provided in various transverse directions, specifically by providing that at least one of the spring bodies has an elliptical outer contour.
In accordance with a concomitant feature of the invention, the a toggle lever is used instead of the plunger.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for varying the spring rigidity of an elastomer mount and a corresponding mount, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.